Interrogation of 1m3 Suspicious Objects via IEC DD Interrogating Neutrons and Tension Metastable Fluid Detectors (#3337)
T. F. Grimes3, A. R. Hagen1, B. C. Archambault2, R. P. Taleyarkhan1, 2
1 Purdue University, Nuclear Engineering, West Lafayette, Indiana, United States of America
This paper describes the development of a SNM detection system for interrogating 1m3 cargo via the combination of a DD neutron interrogation source and TMFD neutron detectors. TMFDs have been shown previously to be capable of using Threshold Energy Neutron Analysis (TENA) techniques to ignore ~2.5 MeV DD neutrons while still remaining sensitive to >2.5 MeV neutrons resulting from fission in the target material. In order to improve the performance of the interrogation, material was added around the accelerator. This material was used to direct neutrons into the package to increase the fission signal, lower the energy of the interrogating neutrons to increase the fission cross-section with HEU, and direct interrogating neutrons away from the detectors in order to lower the required discrimination ratio. Experiments performed with a PuBe source and MnO2 indicated that given optimal source placement and a package void of contents that tremendous gains could be made by placing a paraffin lens between the interrogation source and the package. However, experiments with other cargo fills taken from ANSI N42.41-2007 and sources placed in locations other than the center of the package indicated that other geometries might be superior due to over-focusing and increase of r2 required for the lens. The best performance for the worst case of source location and box fill was obtained by placing moderation only behind the accelerator source rather than in front. Finally, it was shown that there could be significant gains in the ability to detect concealed SNM by operating the system in multiple geometric configurations. Worst case scenarios were created by filling the box with hydrogenous material and placing the source as far away as possible from the accelerator. This was greatly alleviated by modeling moving the accelerator and one TMFD panel to the opposite side. Thus, geometries that are difficult for half of the interrogation time become detected during the other half.
Keywords: TMFD, Neutron, Active Interrogation, TENA, Lens
Evaluation of a Compact Radioxenon Detection System for Support of the Nuclear Test-Ban Treaty (#1940)
S. A. Czyz1, A. T. Farsoni1, L. Ranjbar1
1 Oregon State University, Nuclear Science and Engineering, Corvallis, Oregon, United States of America
Global atmospheric monitoring for radioactive byproducts from nuclear explosions is an essential means whereby the Comprehensive Nuclear Test Ban Treaty Organization (CTBTO) can identify clandestine nuclear weapons tests. Several radioxenon isotopes (131mXe, 133Xe, 133mXe, 135Xe) produced in these tests are key to this endeavor due to a lack of chemical reactivity, ideal half-lives, and unique beta-gamma decay signatures that allow for atmospheric detection in extremely low concentrations. All radioxenon detection systems employed by the CTBTO in the International Monitoring System (IMS) are able to achieve a minimum detectable concentration (MDC) of ≤ 1 mBq/m3 for 133Xe. In an effort to improve upon these systems, a novel radioxenon detection system was designed and tested at Oregon State University. This system utilizes a small plastic scintillator gas cell coupled to an array of SiPMs, which provides a high detection efficiency for conversion electrons and beta particles without significantly attenuating X-rays and gamma rays. The coincident photons are detected by an adjacent coplanar CZT crystal, which maintains excellent resolution at room temperature. The SiPM signal and the CZT signal each undergoes conditioning via a custom PCB, and coincidence events are identified in real-time by a high-frequency FPGA-based dual-channel digital pulse processor. 134Xe, 132Xe, and 130Xe samples were irradiated in the OSU TRIGA reactor and individually injected into the system. A spectrum was taken for each of these isotopes, as well as for background, from which ROIs and MDCs were determined. The prototype system was shown to meet the CTBTO standard of ≤ 1 mBq/m3 sensitivity for both 133Xe and 133mXe. These calculations, MDC estimates for expanded versions of the detection system, and comparisons to other state-of-the-art radioxenon detection systems will be discussed.
Keywords: Radioxenon, CdZnTe, SiPM, Beta-Gamma Coincidence, CTBTO
Fast and thermal neutron detectors for radiation portal monitors (#2072)
M. G. Paff1, S. D. Clarke1, R. T. Kouzes2, S. A. Pozzi1
1 University of Michigan, Nuclear Engineering and Radiological Sciences, Ann Arbor, Michigan, United States of America
Radiation portal monitors (RPMs) can include thermal or fast neutron detectors or a combination of the two. Nearly all current RPM designs contain only thermal neutron detectors, predominantly 3He proportional tubes, in order to detect the spontaneous fast neutron emissions from special nuclear material (SNM) as an elevated count rate above the low natural neutron background. The spontaneous fission neutrons emitted by SNM isotopes are emitted at fast energies on the order of MeV. Thermal neutron detector materials, such as 3He, exhibit their highest interaction cross-sections at much lower thermal neutron energies, below the Cadmium cutoff energy of 0.5 eV. Therefore, 3He tubes are embedded in a low Z moderator, such as high density polyethylene (HDPE), to allow for neutrons to thermalize, thus increasing the system detection efficiency. For SNM hidden in cargo containers, the surrounding environment, such as cargo or a designed shield, will act as an additional moderator. 3He tubes in RPMs therefore are often slightly under-moderated to account for the presence of other moderating material. Fast neutron detectors, such as liquid or plastic organic scintillation detectors or crystalline organic scintillators like stilbene, are typically insensitive to neutrons below 400 keV in energy but are very efficient for higher energy neutrons. Through a series of measurements and simulations of a 252Cf spontaneous fission neutron source with 3He and organic liquid scintillation detectors and stilbene, the effects of varying thicknesses of HDPE shielding are studied. For some shielding scenarios operational benefits might exist for using fast neutron detectors instead of or in addition to thermal neutron detectors. The goals of this study are to identify shielded SNM scenarios for which RPMs might benefit from the addition of fast neutron detectors and to quantify those gains in terms of neutron detection efficiency.
Keywords: radiation portal monitors, neutron detection
Wearable Boron-Coated Straw Directional Neutron Detector with Spectroscopic Gamma Capability (#3557)
J. L. Lacy1, A. Athanasiades1, N. S. King1, C. S. Martin1, R. Nguyen1, G. J. Vazquez-Flores1
1 Proportional Technologies, Inc., Houston, United States of America
Ultra low-profile, pie-shaped boron-coated straws (BCS) have direct applications in wearable neutron detectors for special nuclear material (SNM) safeguard and search missions. Here we present a functional, light-weight and covert belt pack detector populated with 4 x 50 x 100 mm3 panels that provide directional tracking of neutron sources. The 0.128” OD boron coated straws within each detector panel are manufactured with thin radial septa walls to increase thermal neutron sensitivity to 30%, or an equivalent of 10 atm of 3He in the same package. A low-cost, low-power (100 uA) electronics package within each panel provides high voltage, signal amplification, and a CPLD for data analysis. A master control unit provides one month of power (3.7 V) to the 12 detector panels and analyzes the 12 data streams before transmitting information to the user’s mobile phone/tablet device via low energy bluetooth. The distribution of panels around the user’s torso and albedo response provide directional tracking information, with the option for full 3D directionality if two belt packs are utilized. Recently, a spectroscopic CsI(Tl) gamma detector has been integrated for expanded search and characterization capabilities.
This work was supported by the Defense Threat Reduction Agency (DTRA), under Contract No. HDTRA1-14-C-0047, and Alion subcontract no. SUB1213349. The views, opinions, and/or findings expressed are those of the authors and should not be interpreted as representing the official views or policies of the Department of Defense or the U.S. Government.
Keywords: boron-coated straws, neutron detectors, gamma spectroscopy, wearable detectors
Handheld Neutron Scatter Camera for Imaging Special Nuclear Material (#2553)
M. L. Ruch1, W. M. Steinberger1, N. P. Giha1, M. A. Norsworthy1, P. Marleau2, S. A. Pozzi1
1 University of Michigan, Nuclear Engineering and Radiological Sciences, Ann Arbor, Michigan, United States of America
A handheld neutron scatter camera has been developed for treaty verification and emergency response applications. The system is based on stilbene bars coupled to silicon photomultipliers. The device is calibrated through a series of collimated measurements for position sensitivity, backscatter-gated measurements for energy resolution, and a time-of-flight measurement to determine neutron scatter response. Experimental imaging and spectroscopic results are presented for a measurement of fission sources. These results demonstrate the handheld neutron scatter camera’s ability to locate and characterize special nuclear material.
Keywords: Neutron Scatter Camera, Stilbene, Silicon Photomultipliers, SiPMs, Special Nuclear Material, SNM, Treaty Verification, Emergency Response, Imaging
A novel, fast readout, gamma detector system for nuclear fingerprinting (#2853)
A. Giroletti1, J. J. Velthuis1, T. Scott1
1 Bristol Univeristy, School of Physics HH Wills Physics Laboratory University of Bristol Tyndall Avenue, Bristol, United Kingdom, United Kingdom of Great Britain and Northern Ireland
Decommissioning of legacy nuclear facilities or clean up in the aftermath of a nuclear incident requires a detailed knowledge of the amount, type and distribution of nuclear materials present. One technique available to rapidly provide this information in situ is high precision gamma spectroscopy. Spectrometers rely on precision measurements of energy deposited into the spectrometer from incident photons, however the high precision limits the speed of the measurements and therefore limits the upper threshold of radiation levels that can be measured. In this work, we present a novel, multi-detector system with a fast readout (10 times faster than systems currently on the market) that is suitable for higher radiation levels. The device consists of a matrix of 5 sensor materials (Silicon, Gallium Arsenide, Uranium Dioxide, Cadmium Zinc Telluride and Diamond) and exploits the differences in photon cross section of these materials. These differences yield a different number of electron-hole pairs for photons of the same energy in different materials. Hence, measuring the number of signals over specific thresholds in each material allows measurement of the photon energies and thus identification of the source isotope and a comparison of the outing rates in the sensors allows to extract the abundance of the isotope. The readout of the prototype uses the Amptek A250 charge sensitive preamplifier followed by a MAROC3 readout chip; preliminary measurements show a noise level less than 13 mV. The validity of this concept was proved using Monte Carlo simulation. The complete system is now under test. Results of the Monte Carlo study and the device will be presented.
Keywords: solid state radiation detection, dosimetry, nuclear forensics